This invention relates to display boards such as boards of the type used by electrical power companies to display representations of power lines and switches on a map of the territory. Prior art display boards of this particular type have been relatively expensive, difficult to update, or of poor graphic quality.
One prior art system utilizes plastic squares or tiles that are mechanically snapped into special frames to form a graphic mosaic. These tiles are typically 1" square. Standard graphics and symbols are applied to each square by etching, silk screening or other convenient technique, and the tiles are selected and assembled to form the desired image. Thousands of such tiles are required in a typical display board. Thus the board is generally used to depict transmission or distribution systems in a schematic format rather than a geographic format, which requires a resolution not easily achieved by such tiles. Lamp tiles incorporating light emitting devices have been used for producing special effects on such prior art display boards.
Another prior art display board used for representing electrical power distribution systems comprises a steel peg board painted to represent a geographical background. Power distribution equipment is represented by applying pieces and strips of tape to the painted board.
Display boards are well-known outside the electrical power industry and have many applications as for instance in personnel training courses, process control and railway switching. Such prior art displays are commonly printed on a large translucent plastic sheet which may be backlighted as taught by Koch, U.S. Pat. No. 3,608,222. Graphics for such a display have been painted directly on the front face of a panel board or on a subpanel which is subsequently mounted onto the panel board. Silk screening has been employed to improve the straightness and sharpness of lines but has been thought to be prohibitively expensive. For an overview of graphic systems as applied to process instrumentation, reference may be made to an article by Allen Devrishian entitled Graphic System Techniques, Instruments And Control Systems, Vol. 34, pages 1458-1461, August, 1961.